Touch technologies are commonly used as input devices for a variety of products. The usage of touch devices of various kinds is growing sharply due to the emergence of new mobile devices such as Personal Digital Assistants (PDA), tablet PCs and wireless Flat Panel Display (FPD) screen displays. These new devices are usually not connected to standard keyboards, mice or like input devices, which are deemed to limit their mobility. Instead there is a tendency to use touch sensitive digitizers of one kind or another. A stylus and/or fingertip may be used as a user interaction.
U.S. Pat. No. 6,690,156 entitled “Physical Object Location Apparatus and Method and a Platform using the same” and U.S. Pat. No. 7,292,229 entitled “Transparent Digitizer” both of which are assigned to N-trig Ltd., the contents of both which are incorporated herein by reference, describe an electro-magnetic method for locating physical objects on a FPD and a transparent digitizer that can be incorporated into an electronic device, typically over the active display screen. The digitizer sensor includes a matrix of vertical and horizontal conducting lines to sense an electric signal. Positioning the physical object at a specific location on the digitizer provokes a signal whose position of origin may be detected.
U.S. Pat. No. 7,292,229 further describes a passive electro-magnetic stylus which is triggered by an excitation coil to oscillate at a resonant frequency. The oscillating signal is sensed by the digitizer. The stylus may operate in a number of different states including hovering, tip touching, right click mouse emulation, and erasing. The various states may be identified by dynamically controlling the resonant frequency of the stylus so that the stylus resonates at a different frequency in each state or by introducing different modulations to the oscillating signal for each state.
US Patent Application Publication No. 20080128180, entitled “Position Detecting System and Apparatuses and Methods for Use and Control Thereof” assigned to N-Trig Ltd., the contents of which is incorporated herein by reference, describes different embodiments for a stylus including a pressure sensitive stylus where the oscillation frequency of the stylus is modified depending on user applied pressure to the stylus.
U.S. Pat. No. 7,372,455, entitled “Touch Detection for a Digitizer” assigned to N-Trig Ltd., the contents of which is incorporated herein by reference, describes a detector for detecting both a stylus and touches by fingers or like body parts on a digitizer sensor. The detector typically includes a digitizer sensor with a grid of sensing conductors, a source of oscillating electrical energy at a predetermined frequency, and detection circuitry for detecting a capacitive influence on the sensing conductor when the oscillating electrical energy is applied, the capacitive influence being interpreted as a touch.
US Patent Application Publication No. 20050189154, entitled “Noise Reduction in Digitizer Sensor” assigned to N-Trig Ltd., the contents of which are incorporated herein by reference, describes a method for noise reduction in a digitizer, the digitizer comprising a plurality of detecting elements for detecting an electromagnetic signal at one of a number of predetermined frequencies. The detector can be used both for finger touch sensing and for detection of an electromagnetic stylus. In some embodiments described, the noise to be reduced originates from a finger or hand that is touching the digitizer during stylus detection. The method includes sampling at least two detecting elements substantially simultaneously to obtain outputs therefrom, and reducing the output on one of said two elements in accordance with the output on the other of said elements at a frequency other than a pre-determined frequency associated with the stylus.